2499. Imaging of Large Soft Tissue Myxoma with Pathologic Correlation
Authors * Denotes Presenting Author
  1. Jennifer Ficke *; Walter Reed National Military Medical Center
  2. Mark Murphey; Uniformed Services University
  3. Stephen Savioli; Walter Reed National Military Medical Center
  4. James Jelinek; Washington Hospital Center
  5. Alexander Galifianakis; Walter Reed National Military Medical Center
To describe the radiologic appearance of large soft tissue myxomas with pathologic correlation and identify the cause of these larger lesions.

Materials and Methods:
We retrospectively reviewed available demographics, imaging and pathologic material from 15 cases of pathologically proven large soft tissue myxomas (>5 cm maximal dimension) from our archives. Radiologic evaluation was performed by two musculoskeletal radiologists and one fellow with agreement by consensus. Imaging radiographs (n = 3), PET/bone scintigraphy (n = 2), ultrasonography (US, n = 5, Doppler n = 3), CT (n = 3), MRI (n = 15) was evaluated for intrinsic characteristics (i.e., typical features previously described for myxoma), and the cause for large size and was correlated with pathology.

These lesions represented 42% of myxomas from our archives. Demographics, lesion location and imaging characteristics were similar with prior descriptions of soft tissue myxoma. Imaging features included well-defined intramuscular mass with high water content (100%), small amount of surrounding fat (90% on MRI), surrounding edema (95% on MRI) and MRI contrast enhancement patterns. Cyst formation was more common than previously described and was identified in 100% of cases with adequate imaging. In lesions >10 cm in size (n = 4) cyst formation was the dominant component (>75% lesion volume) with the myxoma element <25% of the lesion volume. The myxoma component in these lesions could only be differentiated from the dominant cyst component on postcontrast MRI, US, or T2 nonfat suppressed sequences.

Size >5 cm should not exclude the diagnosis of soft tissue myxoma, which represented 42% of cases from our archives. Large soft tissue myxomas maintain the intrinsic imaging characteristics previously described. Lesions >10 cm are caused by large dominant (>75% of the lesion volume) cystic areas with a small (<25% of the lesion volume) component of myxoma. Postcontrast MR images are optimal to distinguish these components and biopsy must be directed at this smaller component for accurate pathologic diagnosis.